The production of compact heat exchangers using very small flow passages has yielded highly variable results due to the fact that conventional fabrication methods cannot be controlled sufficiently well to yield consistent flow passage dimensions. Compact gas-gas heat exchangers are usually of the plate-fin type and are fabricated from thin sheets of material or plates to which are bonded, such as by furnace brazing, thin fins which are fabricated from strips of the same material used for the plates. The strips and a sheet of braze foil are tack welded together prior to firing the assembly in a braze furnace. The tack welding of the many hundreds of fins is usually done by hand. Manifolds are usually welded to pre-inserted weld stubs which are included with the braze assembly. When the assembly of very small flow passage heat exchangers is attempted, distortion of the thin sheet-metal fins, weld splatter, and braze drop through form significant and uncontrollable flow path obstructions.
Structural improvements in such heat exchangers are desired to enhance the ease of manufacture and reduce complexity while maintaining or improving durability and reliability. Design flexibility is also important to allow selection of the number of passages, etc. with minimal change in the structure and the manufacturing process.